Photodynamic therapy (PDT) is a medical treatment involving the use of a photosensitizing agent which is exposed to a specific wavelength of light to create oxygen radicals, resulting in the destruction of cancer cells, bacteria, viruses or fungi. A PDT system consists of three principal components: a photosensitizing agent, a light source (typically a laser) and a light delivery means (typically optical fiber based).
PDT involves the use of a photosensitizing agent that is relatively selectively concentrated in cancer cells or microbiological pathogen sites. Depending on the type of photosensistizer, it may be injected intravenously, ingested orally or applied topically. After application of the photosensitizing agent it is selectively retained by diseased tissue so that after a period of time, determined by the kinetics of the compound's distribution, there is more photosensitizing agent absorbed by the diseased tissue than in normal tissue. The photosensitizing agent is then activated by exposure to a specific wavelength of light matching the absorption rates. This results in tissue necrosis via several mechanisms including oxygen radical production as well as vascular shutdown to the diseased tissue. Because there is less photosensitizer in the adjacent normal tissue, only the diseased tissue necroses and the normal tissue is preserved when the correct light dose rate for that tissue is administered. The advantage of PDT over conventional treatment such as surgery, radiation and chemotherapy is its relatively selective destruction of diseased tissue with normal tissue preservation.
The light distribution properties of the light delivery device can have direct impact on the effectiveness of the light application and thus the efficacy of the PDT treatment. The challenge of the light delivery devices is to ensure the light distribution is equal along the entire length of the light emitting section of the device. Several types of distributing devices have been developed in attempts to more evenly and safely distribute the light and energy radiating from the device used to deliver the laser energy. One type of diffusing device involves a fiber optic microlens which is able to transfer a divergent light beam to a limited area tissue area. A light diffusion device, as disclosed in U.S. Pat. No. 4,660,925 to McCaughen, Jr. consists of a fiber cylindrical diffuser which emits a cylindrical scattering pattern of light output with respect to the cylindrical axis of the optical fiber, using a spaced series of rings of varying intensity light. Yet another diffusion device as disclosed in U.S. Pat. No. 4,693,556 to McCaughen, Jr. consists of a fiber optic spherical diffuser or “light bulb” which produces a spherical scattering light field. Each of these diffusing devices produces a light field of varying intensity over the area of emitted light from the optical fiber which may result in an uneven activation of the photosensitizer over the treatment area. In still another device, as disclosed in U.S. Pat. Nos. 5,536,265 and 5,695,583 to van den Bergh et al., the cladding is removed from a plastic optical fiber and replaced by a scattering medium which may or may not be roughened, resulting in a light emission area. This device is problematic in that the distal area of the light emitting area is less intense than the more proximal areas of the light emitting area of the device. What is clearly needed, then, is an improved optical fiber that is able to more evenly deliver light energy over a wider surface area.
It is understood that the present invention as described and claimed herein can be used for many additional purposes, therefore the invention is within the scope of other fields and uses and not so limited.